Thermionic tube



May 6, 1941. w. w. EITEL ETAL THERMIONIC TUBE Filed Sept. 26, 1939 H wLw EL, w Y @Esrn CWM M TN.. o WWA ,m mw M um m TH Patented May 6, 19141;

UNITED STATES PATENT oei-ice 'rnsmvnomo TUBE William W. Eifel and JackA. McCullough,

' San Bruno, Calif.

Application September 26, 1939, Serial No. 296,610

;(Cl. Z50-27.5)

4 Claims. Our invention relates to a discharge tube having a cathodestructureV in which electrons are` evaporated from a heated filament;and itis among the objects of our invention to provide improved meansfor supporting `and tensioning the filament.

AAnother object is to provide a cathode structure embodying a filamenttensioning spring disposed outside the intense heat zone in the'tube toprevent heat from deteriorating the spring so that the life of thelatter is preserved for maintaining a constant predetermined tension inthe filament.

Further objects include the provision of irnproved means for mountingthe grid and plate of a thermionic tube, and of means for cooling theplate supporting structure.

The invention possesses other objects and features of advantage, some ofwhich, with the foregoing, will be set forth in the followingdescription of our invention. It is to be understood that we do notlimit ourselves to this disclosure of species of our invention, as wemay adopt variantembodirnents thereof within the scope of the claims.

Referring to the drawing:

Figure 1 is a side view, partly in section and partly in elevation,showing a thermionic tube embodying the improvements of our invention;and

Figure 2 is a detail sectional view of the cathode structure on largerscale.

In thermionic tubes having cathode structures comprising wire laments aproblem arises due to the fact that the filaments expand and warp whenheated unless they are maintained under constant tension. Variousarrangements of springs have been employed to tension the laments, butexperience has proven that the springs in past structures have rapidlydeteriorated under the intense heat developed in the tubes. We haveovercome this difculty by providing a cathode structure in which thespring is disposed outside the intense heat zone in the tube, so thatthe spring maintains its resiliency throughout the life of the tube.Another problem in thermionic tubes is that of keeping the platesupporting structure reasonably cool. In our improved device thestructure is designed to maintain the temperature of the parts withinsafe limits.

In terms of broad inclusion, the thermionic tube of our inventioncomprises an envelope enclosing a cathode structure including a lamentand means for supporting it. A spring for tensioning the lament isinterposed in the supporting means, and the latter is designed to locatethe spring outside the intense heat zone inthe envelope. Improved meansare also provided for mounting a grid and plate in the envelope; theplate mounting being particularly designed for cooling the supportingparts.

In greater detail,I and referring to the drawing, the thermionic tubeembodying our invention comprises a glass envelope 2 having a suitablebase 3 with filament terminal prongs 4. A reentrant stem 6 is providedat the top of the envelope for the anode structure, and a stem 'I isarranged at the base of the envelope for the cathode structure.

`The cathode preferably comprises a pair of hairpin laments 8 ofthoriated tungsten secured at their lower ends to cross bars 9 fastenedto the upper ends of a pair of tungsten rods II projecting upwardly froma pinch I2 of stem l. Suitable leads I3 are connected between the lowerends of these rods and the terminal prongs 4. The upper ends of thefilaments are held by a cross arm I4 mounted on a centrally disposedsupporting rod or standard I6 projecting upwardly from the stem l.

Supporting arm I4 engages the bights of the filaments and is slidablymounted on standard I6 so that upward pressure on the arm tensions thelaments. A coil spring I 1 of suitable material, such as tungsten, isdisposed coaxially about the lower portions of the standard, well belowthe lament. This spring is a suitable stop and the lower end of acoaxial sleeve I8 which slidably embraces the standard and projectsupwardly to bear against the underside of filament supporting arm I4.The ends of the spring are seated in cup-shaped pieces Ii; and a clip 2|fastened to standard i6 forms the stop for the lower end of the spring.These parts as Well as the sleeve I8 and arm I 4 are preferably made ofa formable heat resistant material, such as tantalum.

By this arrangement the spring I' is disposed outside the intense heatzone adjacent the lament, and the spring is therefore not deterioratedby the heat generated in the tube. If desired, the spring may be loweredto rest on the stem 1, thus removing it still further from the heatzone. Ordinarily such distant spacing is not required however and thespring may safely be disposed further up along the standard, as shown inthe drawing.

Grid 22 of our tube is disposed coaxially about the cathode-structureand is supported by a ring compressed between forms a cavity 32 opening;out to the atmosphere.

for ventilation, and the upper ends of rods 28 are connected to enlargedrisers 33 of a good heatY conducting material such as copper to rapidlyconvey Vheat from theV stem structure. risersI are connected to aterminal button also preferably of copper.

In larger tubes, Where are quite heavy, heat the rods adjacent theplate, as by tapering-their lower ends 36.. This permtsthezuseoiIsiiiic;lient-. ly heavy rods for rigidity, yettends'to thermallyisolate the plate.

For further cooling the stem structure 4We ,DIO-

vide an aperture31 irrterniinal,buttonfland,

make connection with a suitable b lowerethrough a exible duct 38 fordirectingastream of; coole..

ing fluid or airpintoethe cavityof thestem, By

employing a exible duct of electrical conducting e materialthis ductmayA alsoserve. as theaplate s lead. If" desired, cooling nsmaybe.provided.

onterminal button, either formedas: an integral part of the. buttonoregon a separatesleeve encirclingV the button.

Another cooling feature in ourtube; associated with the cathodestructure, theoprojection .of

the vlovver end.. of. standard.- I BL into theaairr space The standardor rod. lithus. also Afunctions as a heatconducting. member foriv ofhollow stem 1.

'filesetv the plate supporting rods conduction from the-plate, may beretarded by reducing the cross-sectionoi conveying heat from the cathodesupporting structure to a point outside the envelope. It is also to benoted that spring I1 is disposed adjacent the lower or heat dissipatingend of the standard, so that the spring gets full benefit of thecooling.

We claim:

1. In a thermionic tube, a cathode structure comprising a filament, aYstandard,V a filament supporting arm slidable on thestandard, a sleeveembracing the Standard and bearing at one end against said arm, and aspring surrounding the standard and bearing against the other end of thesleeve for tensioning the filament.

2, Inparthermionic tube, a cathode structure comprising a'hairpiniilament, a standard, a supporting arm slidable on the standard andengagingthe bightoffthelament, a sleeve embracing thestandvard andbearing at one end against said arm', anda spring encircling thestandard and bearing., against; the,v athen-endl of the; Sleevel fortensioninsrthe iilamentf looting..-` upwardlye; from the base of'V theetub supporting arm slidable on easing, the..bight; of, the lament, asleeve embracing: .the standardandxtenclina downvlardly v from saidarm., and,aespringencirclingtne stand.- ard andk bearing against.,ythe.y lower end of. the sleeve for tensioning thefiilament- 4.a In athermionicltube, afcathodestruotu-re comprising a filament, a lamentengagingle.- ment, a standard,Av a-compressiongmernber `slidable alongsaid standard` andlbearng against said element, andaspringbearingragainstfsaidimemf ber for tensioning therfilament. Y

W1LLIAM-.W- vllITiilLi.

JACK;V Ar. lvicoUi.Londra` ..0 time, `4a y Cathode, structure.comprising a. hairpin; filamenti a; Standard-1Dro:`

the standard, anden-,N

